1. Field of the Invention
The present invention generally relates to compositions and methods for increasing muscle mass, strength, and functional performance in the elderly. In particular, the compositions consist of a selection of amino acids including leucine, carnitine, and carbohydrates with low glycemic index.
2. Description of the Related Art
As the population ages, and in particular as the “baby boomers” grow into their old age, the health problems associated with aging grow increasingly important This is particularly true in a health system such as the current one where health care costs are distributed across the population; the increased prevalence of aging-related health problems will result in generally increased costs to all. In addition, reactive health care is more expensive than preventative health care; for example, fixing broken bones or replacing a hip after a fall by a frail patient is more expensive than preventing that fall by decreasing the patient's frailty. For these and other reasons, it is desirable to have effective, relatively inexpensive means for preventing and ameliorating some aging-related health problems.
One such health problem may be referred to as “sarcopenia.” As used herein, the term “sarcopenia” refers to the loss of muscle mass and function that inevitably occurs with aging. Sarcopenia is responsible for decreased levels of physical activity which, in turn, can result in increased body fat and a further loss of muscle. Loss of muscle mass results from a negative net balance between muscle protein synthesis and muscle protein breakdown. The etiology of this loss of skeletal muscle mass and function is not believed to be clear. Reduced levels of physical activity, loss of motor units secondary to changes in the central nervous system, and inadequate protein intake have all been implicated.
Sarcopenic individuals, in their relatively weaker state, may be more prone to falls and injuries from performing bodily tasks that may have been performed more easily when they had greater muscle mass and function. They also may have decreased bone and joint health, which further limits mobility. Because sarcopenia increases risk of injury, decreases mobility and quality of life, and causes other problems, it is desirable to effectively, noninvasively, and relatively inexpensively prevent or ameliorate sarcopenia and increase muscle mass, strength, and physical function, especially in the elderly.
Stimulation of muscle protein synthesis is believed to be the metabolic basis for increased muscle strength. An increase in muscle protein synthesis can increase muscle mass, which is related to strength. Increasing muscle protein synthesis also increases muscle protein turnover (i.e., the combination of protein synthesis and breakdown), since the rate of breakdown is believed to be related to the rate of synthesis to some extent. Increased muscle protein turnover increases the functioning of muscle fiber units, because the older, damaged proteins are replaced by newly produced proteins that function more efficiently. Thus, a method to increase muscle protein synthesis and muscle protein turnover may achieve the goal of increasing muscle mass, strength, and physical function.
There are believed to be four central components to the stimulation of muscle protein synthesis. The capacity of the synthetic apparatus of the cell must be activated by a series of factors collectively referred to as eukaryotic initiation factors. The availability of all the component amino acids needed for the synthesis of the new proteins must be increased, and transfer RNA (tRNA) molecules must transfer those amino acids effectively from the intracellular free pool to the site of synthesis in the ribosome. Finally, there must be adequate energy available, in the form of adenosine-triphosphate (ATP), for all the necessary reactions to proceed. In sum, increased physical function requires not only adequate muscle mass and function of the muscle fibers, but also the energy needed to support muscle contraction. Energy can be stored in the cell as ATP and creatine-phosphate (CP). Synthesis of ATP is believed to be promoted by the provision of ribose, and creatine is believed to promote the storage of energy in the form of CP.
By addressing any or all of these four components, muscle protein synthesis can be increased either pharmacologically or through nutrition. Pharmacological interventions (e g, testosterone) can be effective, but all have significant undesirable side effects and require medical supervision. In contrast, nutritional compositions are desirable because they are noninvasive and may be designed to minimize such side effects, and may become a part of an individual's routine without such medical supervision.
There are currently no nutritional compositions designed to specifically promote muscle protein synthesis in elderly individuals, or more generally to improve strength and functional performance in elderly individuals. Current nutritional compositions are not believed to have sufficient leucine to effectively accomplish the goals stated herein, alone or in combination with muscle-building compounds such as creatine. For example, whey isolates currently comprise between about 6 and about 9% leucine; this is not believed to be sufficient to achieve improved muscle mass, strength, and functional performance in the elderly.
A high percentage of elderly individuals suffer some degree of renal insufficiency, often at the sub-clinical (and thus undiagnosed) level. Impaired renal function is common in individuals with sarcopenia, so nutritional approaches to resolving sarcopenia must not compound this potential problem by increasing the load of urea that the kidney must excrete. A high intake of protein could potentially amplify this problem by causing a significant increase in urea production, thereby putting an increased burden on the kidney by requiring increased urinary excretion. It is therefore desirable for any composition for supporting synthesis to minimize renal burden.
The effect of increased protein intake on bone health has been debated. On the one hand, protein synthesis is essential for bone health and is stimulated by increased protein intake. Since collagen is a major protein component of bone and glycine constitutes about 30% of collagen, it is desirable for a composition promoting bone synthesis to contain sufficient glycine and other amino acids to stimulate collagen synthesis in bone. On the other hand, ingestion of sulphur-containing amino acids, particularly cystine and cysteine, causes the production of sulfuric acid in the course of their metabolism. Increased sulfuric acid acidifies the blood and accelerates loss of calcium from bone. It is therefore desirable for such a composition to circumvent this response by not including either cystine or cysteine, as neither of these amino acids is believed to be necessary for stimulation of muscle protein synthesis.
An additional difficulty with nutritional supplements for older adults is that older adults generally compensate for increased energy (i.e., calories) delivered by nutritional supplements by reducing food intake. It is therefore desirable to design a supplement that stimulates muscle synthesis more efficiently than food or common protein supplements.